Effects of He on Cu film formation by rf sputtering

Cu films have been deposited at room temperature by the rf sputtering using a gas mixture of Ar and He in order to investigate the effects of He gas o n film formation by sputtering. The plasma diagnosis was performed as a pre liminary experiment by the single probe method and the optical emission spe ctroscopy analysis for the He+Ar sputtering plasma. From the results, it wa s found that the electron density increased by mixing He gas with the sputt ering Ar gas, suggesting that Ar+ ions increased. This indicates that Ar+ i ons are effectively generated by collision with He-m atoms in neutral excit ed metastable states with high energies through the Penning ionization proc ess, so that the deposition rate of Cu films increased. For Cu films deposi ted using the He+Ar gas, the preferential growth of a (111) plane was obser ved. The film surfaces of Cu films deposited using the He+Ar gas were smoot her than those deposited using the pure Ar gas. The films deposited using t he He+Ar gas were conductive even at thickness less than 5 nm and have lowe r resistivities than those deposited using the pure Ar gas. These results s uggest that the migration of Cu atoms on film surfaces is enhanced by an in crease in an amount of Ar+ ions which bombard the Cu film surface. (C) 1998 Elsevier Science Ltd. All rights reserved.